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26 PCB007 MAGAZINE I MAY 2019 and adhesiveless options from 0.5–5 mils, and copper is available from 0.25–2 oz. Other thick- nesses are available, but these are the most widely used. From there, it is important to re- search what you preferred fabricator regularly stocks. Each fabricator stocks a group of mate- rials based on existing customer demand and preferred materials. If you can create a stackup around those materials, it will save time and project costs. Flexible coverlay options are also something that is asked about frequently. There are two primary options. First, and most common, is polyimide film-based coverlay. This option is highly recommended for dynamically flexing applications and rigid-flex. It is important to specify the adhesive thickness in accordance with the copper height on the base laminate to ensure full encapsulation. Another option for flexible cover coat is flexible photoimaga- ble coverlay. This option provides a better res- olution for dense SMT component areas and produces crisp, square SMT pad openings. But while this material is flexible, it is not intend- ed for dynamically flexing applications. If you need dense SMT pad openings on flex, laser- skived, polyimide-based coverlay is an excel- lent solution. It is a bit more expense than drilled or routed coverlay, but it is a viable op- tion when those things are critical. I am also frequently asked about ALD ink supporting the semi-additive process (SAP) do- mestically. This process has been proven with prototypes and is on the cusp of transitioning to production in North America. This is an ex- citing new chemistry that enables line width and space at 0.001" and below. Numerous ap- plication areas are investigating how to in- corporate this technology, and fabricators are exploring how to bring this process on-line to meet those needs best. Over time, this will be quite the game changer for the PCB industry by reducing layer count and lamination cycle requirements as well as supporting the tech- nology needed for increasing complex pinouts. The previous technologies are areas that I am familiar with. But, as I mentioned in the in- troduction, I am also consistently asked about processes and materials that are new to me. Copper coin technology is not something that I have been familiar with. After seeing an ap- plication that was built with this technology, I did a little research and learned that it is used to dissipate heat when thermal vias or metal core materials are not sufficient. The concept is based on getting a copper coin press-fit into a premade cut-out in the board directly under the area that is a hot spot. Interesting! What an exciting time to be in this indus- try. There are so many new processes and materials in the PCB segment that it can be a challenge to keep up with all the new de- velopments. It is fun to start chasing the next new thing, but I also think it is important to keep in mind that even materials and process- es that have been around for a while are still new to someone. Not everyone has used flex materials or copper coin technology, and only a select few have used additive processes for PCB fabrication. Thank goodness our industry is supported by strong technical publications and industry events to help us all learn about technology that is new to us and help us build a strong network of people to reach out to with questions. PCB007 Tara Dunn is the president of Omni PCB, a manufacturer's rep firm specializing in the PCB industry. To read past columns or contact Dunn, click here. Each fabricator stocks a group of materials based on existing customer demand and preferred materials. If you can create a stackup around those materials, it will save time and project costs.

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